Microemulsions are nanostructured dispersions that have unique properties, which make them attractive for applications such as biomaterials, drug delivery, and nanoparticle synthesis. The behaviour of hydrocarbon microemulsions and their applications have been extensively studied, however, there have been very few studies in the preparation or the polymerization of silicone microemulsions. Silicone microemulsions offer a unique template by which to create novel nanoporous silicone elastomers and/or hydrogels. The prevalent use of silicones in biomaterials, coatings, and personal care (to name a few) make the development of silicone-based microemulsions of particular interest. The aim of thesis research was to polymerize silicone microemulsions and to understand the factors that contribute to retaining initial template morphology in the polymeric product. Chapter Two of this thesis focuses on the preparation of silicone microemulsions containing a non-polymerizable and polymerizable trisiloxane surfactant, respectively. Formulations were prepared and characterized by electrical conductivity to determine the microemulsion structure type. Formulations located in the bicontinuous region of the phase diagram were polymerized, producing transparent silicone elastomers. The focus of Chapter Three was to determine the tolerance of silicone microemulsions to selected chemistry that is relevant to silicone polymers. Previous work done in the field of polymerizing silicone microemulsions has been based on radical polymerization processes. There are no reports that examine the polymerization of a silicone microemulsion by room temperature vulcanization (RTV), a common process for creating silicone elastomers. We aimed to better understand the effects of RTV cure on morphology retention from the liquid to polymeric product to determine if this type of chemistry could be used in the formation of nanoporous silicone elastomers either on its own or in conjunction with a radical polymerization process. In order to understand the effects of an RTV process on polymer structure, we examined the effect of the variable components (necessary for the RTV cure) on the silicone microemulsion template. Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) were used as tools to characterize materials prior to and after cure. Silicone microemulsions that were cured using the RTV process produced nanoporous polymeric elastomers, however, the initial bicontinuous microemulsion template was not retained. RTV cured microemulsions retained the bicontinuous structure if the RTV cure was preceded by a photopolymerization reaction to “lock-in” surfactant monomers at the oil/water interface. Chapter Four explores the use of silicone microemulsions as a reaction vehicle in the formation of nano-TiO2 particles. The focus of this chapter was the exploitation of microemulsion droplets and bicontinuous structures that were designed to retard TiO2 particle formation in situ. Titanium isopropoxide (TTIP) was incorporated into silicone microemulsions containing varying amounts of water. Interactions between TTIP and the trisiloxane polyether surfactant result in the formation of a compound containing a Ti4+, coordinated to silicone surfactant molecules via a polyether linkage. Titania forms in situ as water is titrated into the surfactant/oil mixture, resulting in the formation of a microemulsion. The formation of TiO2 was monitored by UV-Vis spectroscopy and the TiO2 particles were characterized using transmission electron microscopy. / Thesis / Doctor of Philosophy (PhD) / This thesis is about the chemical modification and polymerization of nanostructured liquids in the form of silicone microemulsions to create nanoporous silicone elastomers (nano is one billionth, 10-9, so 1 nanometer = 1 billionth of meter). Despite the highly prevalent commercial use of silicones and the utility of silicone elastomers, little is known about the polymerization of silicone microemulsions to create nanoporous materials. The first goal of this thesis was to polymerize silicone microemulsions, using methods that have been previously used in the polymerization of hydrocarbon microemulsions. Silicone microemulsions were successfully polymerized using a reactive surfactant and rigidification of the oil phase was achieved using common silicone crosslinking chemistry. The second goal was to understand how the type of chemistry affects changes in structure upon transition from liquid microemulsion to solid polymer. Nanostructuring was retained in polymerized microemulsions both with and without oil phase polymerization. Finally, the third goal was to exploit silicone microemulsion domains to control titanium dioxide particle formation. Particle formation was slowed as a result of domain constricted particle growth.

Yes / Polymer self-assembly in solution is a simple strategy for the preparation of elegant yet complex nanomaterials. However, exhaustive synthesis of the copolymer synthons is often required to access specific assemblies. In this work we show that the blending of just two diblock copolymers with identical block lengths but varying hydrophobic monomer incorporations can be used to access a range of assemblies of intermediate hydrophobic composition. Indeed, the nanostructures produced from blending are identical to those formed with the directly synthesized copolymer of the same composition. This new approach presents researchers with a more efficient and accessible methodology to access precision self-assembled nanostructures, and we highlight its potential by applying it to a demonstrator catalytically active system. / European Science Foundation (ESF), Engineering and Physical Sciences Research Council (EPSRC), United States. Air Force. Office of Scientific Research (AFOSR)

No description available.

No description available.

M.Sc.(Nanoscience) / The synthesis and application of gold nanoparticles (AuNPs) has been intensively studied worldwide. However, the toxicity of these nanoparticles is still a concern. We considered that various physiochemical methods used to synthesize AuNPs are energy driven, costly and require the use of harmful chemicals. Thus, this makes them not environmentally-friendly. The aim of this study was therefore to synthesize AuNPs via a greener route using Aspalathus linearis tea leaves. The AuNPs were used to coat eight commercial antifungal discs (i.e. amphotericin B, fluconazole, clotrimazole, econazole, flucytosine, ketoconazole, miconazole and nystatin) against four Aspergillus spp. for enhanced antifungal activity. The aqueous extract of A. linearis was characterized by high performance liquid chromatography and liquid chromatography–mass spectroscopy. The AuNPs were characterized using ultravioletvisible (UV-vis) spectroscopy, dynamic light scattering, nanoparticle tracking analysis, Fourier transforms infrared spectroscopy (FTIR), high-resolution transmission electron microscopy and X-ray diffraction. The toxicity of the synthesized AuNPs was studied by 3-(4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay and xCELLigence test on HepG-2 cell lines and results revealed very little to no toxicity of the AuNPs. The pristine antifungal and AuNPs coated antifungal discs were characterized by FTIR, scanning electron microscopy (SEM) and antifungal activity performed using the disc diffusion method. A strong resonance peak was observed at 529 nm of the AuNPs measured using UV-vis spectroscopy. Average size of AuNPs was ~44±1 nm and demonstrated excellent in-vitro stability under various solutions (5% NaCl, phosphate buffered saline) at varying pH levels. The SEM images revealed that the AuNPs were attached onto the coated antifungal discs when compared with the pristine antifungal discs. Antifungal results indicated that AuNPs significantly (p<0.001) enhanced the antifungal activity of the coated antifungal discs against the tested fungi when compared to the pristine antifungal discs. The AuNPs coated econazole disc exhibited the greatest (broad spectrum) activity than other antifungal agents tested. In conclusion, A. linearis can be used as a reducing agent in the synthesis of stable AuNPs. Furthermore, the AuNPs coated antifungal discs demonstrated considerable antifungal activity over the pristine antifungal discs...

The effect of processing temperature on the crystal structure properties of the Fe-substituted Hydroxyapatite (Fe-HAp) was studied by using the Rietveld refinement method of powder x-ray (XRD) and neutron diffraction (NPD) patterns. Superconducting QUantum Interference Device (SQUID) magnetometry, transmission electron microscopy (TEM) and x-ray fluorescence spectroscopy (XRF) were used to study the magnetic properties, particle morphology and chemical composition of the prepared samples. Two sets of samples of chemical formula Ca5-xFex(PO4)3OH were prepared with x = 0, 0.05, 0.1, 0.2 and 0.3 by using processing temperatures of 37°C and 80°C, following a two-step co-precipitation method. A single phase HAp was identified in samples with x = 0 and 0.05. Processing temperature affects the type and percentage of secondary phases: hematite was detected in samples prepared at 37°C with x ≥ 0.1, hematite and maghemite were detected in samples prepared at 80°C with x = 0.2 and 0.3. Rietveld refinements of NPD and XRD patterns showed that the a lattice constants are greater in Fe-substituted samples prepared at 37°C, whereas the c lattice constants are greater in the 80°C samples for x ≥ 0.05. Fe preferentially substitutes at the Ca2 site in the 80°C samples, whereas Ca1 is the preferred substitution site in the 37°C samples. Fe substitution results to a decrease of the lattice constants at both preparation temperatures. The ratios Fe/(Fe + Ca) of the refined atomic fractions of the samples prepared at 80°C are greater than those of the 37°C samples. Further, more secondary phases form in samples prepared at 37°C compared to 80°C samples. The magnetic measurements reveal that pure HAp is diamagnetic, whereas samples with x = 0.05 and 0.1 are paramagnetic. Samples with x = 0.3 showed superparamagnetic behavior based on ZFC and FC measurements. Similar hysteresis loops in samples x = 0.2 and 0.3 indicate that the samples with x = 0.2 may show superparamagnetic properties. For x = 0.2 and 0.3, the samples prepared at 80°C showed higher magnetization compared to the 37°C samples, because of the maghemite secondary phase. Based on the TEM images, Fe substituted HAp nanoparticles prepared at 37°C are mainly spherically shaped, and the 80°C particles are mainly elongated. Increase of the Fe concentration favors formation of elongated particles and larger spherical particles. The XRF measurements confirm the Fe for Ca substitution in the HAp structure based on the decrease of the Ca/P and the increase of the Fe/(Fe + Ca) atomic ratios with the Fe concentration. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection

Atomically thin two-dimensional nanomaterials such as graphene and transition metal dichalcogenides (TMDCs) have seen a rapid growth of exploration since the isolation of monolayer graphene. These materials provide a rich field of study for physics and optoelectronics applications. Many applications seek to combine a two dimensional (2D) material with another nanomaterial, either another two dimensional material or a zero (0D) or one dimensional (1D) material. The work in this thesis explores the consequences of these interactions from 0D to 2D. We begin in Chapter 2 with a study of energy transfer at 0D-2D interfaces with quantum dots and graphene. In our work we seek to maximize the rate of energy transfer by reducing the distance between the materials. We observe an interplay with the distance-dependence and surface effects from our halogen terminated quantum dots that affect our observed energy transfer. In Chapter 3 we study supercapacitance in composite graphene oxide- carbon nanotube electrodes. At this 2D-1D interface we observe a compounding effect between graphene oxide and carbon nanotubes. Carbon nanotubes increase the accessible surface area of the supercapacitors and improve conductivity by forming a conductive pathway through electrodes. In Chapter 4 we investigate effective means of improving sample quality in TMDCs and discover the importance of the monolayer interface. We observe a drastic improvement in photoluminescence when encapsulating our TMDCs with Boron Nitride. We measure spectral linewidths approaching the intrinsic limit due to this 2D-2D interface. We also effectively reduce excess charge and thus the trion-exciton ratio in our samples through substrate surface passivation. In Chapter 5 we briefly discuss our investigations on chemical doping, heterostructures and interlayer decoupling in ReS₂. We observe an increase in intensity for p-doped MoS₂ samples. We investigated the charge transfer exciton previously identified in heterostructures. Spectral observation of this interlayer exciton remained elusive in our work but provided the motivation for our work in Chapter 4. We also discuss our preliminary results on interlayer decoupling in ReS₂.

Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Title from first page of PDF file (viewed March 12, 2010). Available via ProQuest Digital Dissertations. Includes bibliographical references (p. 117-136). Also issued in print.

Central to the practical use of nanoscale materials is the controlled growth in technologically meaningful quantities. Many of the proposed applications of the nanomaterials potentially require inexpensive production of the building blocks. Solution-based synthetic approach offers controllability, high throughput, and scalability, which make the process attractive for the potential scale-up. Growth kinetics could be readily influenced by chemical interactions between the precursor and the solvent. In order to fully utilize its benefits, it is therefore pivotal to understand the decomposition chemistry of the precursors used in the reactions. Supercritical fluids were used as solvent in which high temperature reactions could take place. Silicon nanowires with diameters of 20~30 nm was synthesized in supercritical fluids with metal nanocrystals as seeds for the nanowire growth. To unravel the effect of silicon precursors, several silicon precursors were reacted and the resulting products were investigated. The scalability of the system is discussed based on the experimental data. The nanowires were characterized with various characterization tools, including high-resolution transmission electron microscopy and electron energy loss spectroscopy. The crystallographic signatures were analyzed through the transmission electron microscopic study, and fundamental electrical and optical properties were probed by electron energy loss spectroscopy. Carbon nanotubes were prepared by reacting carbon-containing chemicals in supercritical fluids with organometallic compounds that form metal seed particles in-situ. A batch reaction, in which the temperature control was relatively poor, yielded a mixture of multiwall nanotubes and amorphous carbon nanofilaments with a low selectivity of nanotubes in the product. When reaction parameters were translated into a continuous flow-through reaction, nanotube selectivity as well as the throughput of the total product significantly improved. Magnetic properties of various metal nanocrystals were also studied. Colloidal synthesis enables the growth of FePt and MnPt3 nanocrystals with size uniformity. The as-synthesized nanocrystals, however, had compositionally disordered soft-magnetic phases. To obtain hard magnetic layered phase, the nanocrystals must be annealed at high temperatures, which led to sintering of the inorganic cores. To prevent sintering, the nanocrystals were encapsulated with silica layer prior to annealing. Interparticle magnetic interactions were also explored using particles with varying silica thickness. / text

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.